Long range studies on the in vitro bioactivity of luteinizing hormone and chorionic gonadotropin in man and other species were continued. The recently in vitro bioassay for themeasurement of LH and hCG in serum has been more extensively applied to studies on gonadotropin regulation in man and other species. Studies on the pulsatile release of LH in men and postmenopausal female have demonstrated the value of bioactive LH determinations to analyze serum LH profiles, and indicated that LH is secreted in pulses of high biological activity.